The present invention relates to a cooling device for disc brakes, and more particularly to a guide means for cooling automotive disc brakes by conducting air through and around the disc brakes.
One cooling device for solid disc brakes is disclosed in German Unexamined Published Patent Application (DE-OS) No. 31 20 021. In the '021 specification, a device is disclosed which utilizes a fan wheel to produce an air circulation from the inside of the wheel toward the outside of the wheel. A dish-like cap is provided on the inside of the wheel in order to obtain positive circulation of the air. The dish-like cap partially surrounds the brake unit, and provides a wide spacing between the cap and the brake unit. The cap extends upwardly to the central plane of the brake disc. The air is conducted into the cap via a peripheral influx opening, and is removed from the cap by way of air passage ducts in the base of the brake disc. Additionally, air is conducted toward outer openings on the rim side of the brake disc through the open side of the hub. This known arrangement conducts the cooling air stream generally over only the internal surface and the rims of the brake disc, thereby producing only a unilateral cooling of the brake disc. Only a minor cooling flow is directed toward the friction surface of the brake disc facing the rim recess. Only a minor cooling flow is conducted across the friction surface because there is no positive conductance of air in the region of the friction surface to provide a direct passage of cooling air flow across the friction surface. Rather, the already heated air coming from the inside of the wheel is introduced into the space between the rim recess and the corresponding brake disc surface, so that the air is incapable of providing a substantial cooling action in this zone.
Another cooling device is described in German Unexamined Patent Application (DE-OS) No. 30 25 757. The '757 specification describes a cooling device for an internally vented brake disc of an automotive vehicle wherein air circulation takes place from the outside of the brake disc toward the inside. In this arrangement, the air is conducted through external openings in the wheel hub toward an internal duct between the friction rings of the brake disc. In this design, the cooling air stream is conducted into the inner space of the rim toward the brake unit without any direct guidance. As a consequence, the cooling air stream is distributed in an uncontrolled fashion, thereby providing little cooling for the brake disc.
It is an object of the present invention to provide a cooling device of the above-described type which provides an effective cooling of the brake disc and of the wheel parts which are in heat contact with the brake discs.
In accordance with the present invention, a cooling device is provided for a motor vehicle having a wheel which includes a rim cover portion having at least one opening, a wheel hub having hub air duct through which air can pass, and a disc brake unit including a disc member having first and second friction rings, and at least one radially extending air duct disposed between the first and second friction rings. The cooling device comprises guide means for conducting air into the wheel duct, through the disc brake unit, and out through the wheel rim cover opening for cooling the disc brake unit. The guide means comprises an air guide housing means which generally encloses the disc brake unit, for forming external air ducts externally of the friction rings. The housing means includes influx openings which are positioned for conducting air to the hub air duct, the external air ducts, and the radially extending air duct. Efflux openings are provided which are cooperatively positioned with the wheel rim cover openings to conduct air from the housing means to the rim cover openings.
One aspect of the present invention is that the cooling air stream flows around the brake disc in a space defined by a guide means housing which is placed in generally close proximity to the brake disc. This arrangement promotes the optimum cooling of the brake disc and the removal of heat from all sides of the brake disc, including the outside and the inside of brake discs. To attain an optimum cooling effect, it is advantageous to variably distribute the cooling air around the brake disc. The applicant has found that the quantity of air which is conducted past the outside surfaces of the friction rings is preferably less than the quantity which is conducted past the radially extending internal duct between the friction rings of the brake disc.
The wheel has an outer shape which is designed to produce a relative vacuum situation adjacent the outer portion of the wheel, and a relative overpressure situation adjacent the inside of the wheel. This relative vacuum/overpressure arrangement promotes air circulation through the cooling device. Alternatively, enhanced air circulation can be obtained by providing a fan or suction removal means to promote the flow of air to the cooling device.
One feature of the present invention is that the air guide housing means can be made of a synthetic resin material having adequate temperature stability. This feature has the advantage of enabling the manufacturer to produce the housing means economically.
Another feature of the present invention is that the guide means provides unheated air to several partial air streams, with these partial air streams being fed directly to the individual regions of the brake discs to be cooled. For example, an air stream which is drawn into the influx openings of the device can be subdivided into four partial air streams. Of these four partial air streams, two are conducted to the outer surfaces of the friction rings, and the other two are conducted to the radially extending duct between the friction rings. Additionally, one or more partial air streams can be conducted inside of the wheel through ducts in the wheel hub, which helps to cool the wheel hub and adjoining wheel elements. By dividing the incoming air stream into four partial air streams, each region of the brake disc can be exposed to a cooling air stream which has not been heated by contact with hot portions of the brake or wheel assembly.
It is also a feature of the present invention to provide at least two influx openings which are arranged in the outer part of the housing. These influx openings are preferably located on each side of the wheel hub. An accelerated introduction of cooling air into the device can be achieved by orienting the inlet of the influx openings in opposition to the head wind, to thus obtain and enhance the delivery of cooling air to the openings. This feature has the advantage of enabling the device to deliver a generally uniform flow of cooling air to the brake unit.